A New Soldermask for Eurocircuits’ PCBs.

Last year we made one of the group’s largest investments by installing the Ledia direct imaging system in our plant in Eger – Hungary. We can use Ledia to expose inner layers, outer layers and Soldermask as well. With the Ledia we can produce PCB’s with tighter tolerances on images and Soldermask.

To better optimize all advantages that Direct Imaging of thev Soldermask with the Ledia has to offer, we needed to change the Soldermask to another type. Still from the same supplier, Sun Chemicals, CAWS2708 LDI is better suited for the Ledia’s imaging process.

With this new, professional and reliable Soldermask, we can expose our production panels faster than with the previous type. In combination with Direct Imaging, we can also achieve much better results on registration accuracy.

The surface of the new Soldermask is perfect for soldering. The matt finish helps with the alignment for placing components and it is better suited for automatic optical inspection after soldering. We are convinced that this Soldermask is a modern and user-friendly product.

  

We made lot’s of tests with the new Soldermask and all test results were very convincing. The many micro sections we have made, show that the thickness and coverage of the Soldermask are also very good. We measured at least 10 micron of Soldermask on the edges of the tracks.

The left picture shows the Soldermask we use in Eurocircuits Eger and the right picture shows the Soldermask of Eurocircuits Aachen.

 

In Eurocircuits Aachen we are using the sister product of the CAWS2708 LDI of Sun Chemical. The CAWN2295 used in Aachen has the same RAL colour of the one in Eger and has the same technical features. Nevertheless, there will be optical differences between the two because of the different application method. We use curtain coating in Germany and spray coating in Hungary.

The physical and chemical properties of both Soldermask types are the same after the curing process and both have very good electrical properties. Last but not least we can state that the new Soldermask has excellent characteristics for the adhesion to the copper surface.

To summarize we can conclude that the new Soldermask types we use in Eger and Aachen have better characteristics than what our customers were used to before although they might look a bit different than the previous types.

Eurocircuits Technical Update – direct imaging technology

In this update

  • New direct imaging technology – more capacity, more design options
  • 2015 – a record start to the year
  • Medium-volume BINDI pool now UL approved – and 4 layers soon
  • Eurocircuits sponsor student projects

Direct-imaging technology

MORE CAPACITY

The Ledia V5 direct-imaging system, installed in January, is our largest single investment in a single piece of equipment – and is already paying off. Direct imaging has boosted our production capacity in time to handle the fastest growth in orders we have seen in years. See how it works in our technical BLOG.

MORE DESIGN OPTIONS

The reliable assembly of new-generation BGAs, QFNs and fine-pitch leaded components demands tighter-toleranced soldermasks. Ledia images finer soldermask dams than conventional phototools. We will use it in conjunction with our forthcoming solder-bridge pre-CAM tool to produce the optimum soldermask solution for your designs.

2015 – a record first quarter

Q1-2015 we served more than 5,500 customers with almost 24,000 orders. Thus we are up 15.8% and 18.5% on the first quarter of 2014. And 2014 was already a record year.

BINDI pool news

  • Our BINDI pool service for orders up to 50 m2 is now UL approved. UL marking can be added to your boards at no extra cost
  • From May BINDI pool will offer 4-layer multilayers as well as 2-layer PCBs

Student project sponsorship

We have sponsored student projects across Europe for many years as part of our commitment to foster new generations of electronics designers. See our BLOGS for some recent projects. If you are looking for sponsorship for a student or educational project, contact us at euro@eurocircuits.com.

Technical blogs

Some recent highlights, all now available in English, French. Spanish and Portuguese:

If you would like us to produce a blog or white paper on a particular aspect of PCB manufacturing technology, PCB soldering or EAGLE CAD, email us at euro@eurocircuits.com.

Meet us

The best way to share ideas and knowledge is face to face. Come and meet us at:

How do we assure the quality of your PCB – part 3

Quality assurance –  Microsection analysis

Introduction

Microsectioning or cross-section analysis is a destructive sample testing procedure, used throughout the PCB fabrication industry. We make regular microsections each day, as they allow us to see inside the PCB and make precise measurements to check our production processes and to confirm the quality of the finished PCBs.

We use microsectioning to check the quality of:

  • PCB base material
  • inner structure of multilayer boards
  • plating in plated-through holes
  • thickness and registration of external and internal conductors
  • connection between the layers
  • soldermask cover
  • surface finish thickness

Microsectioning procedure

  1. Select the appropriate PCB or quality-control test coupon
  2. Cut out a piece for sample
  3. Embed the sample in resin
  4. Grind down to a flat surface
  5. Polish and etch back if needed

Multilayer build checking

We check the build-up of the multilayer PCB, the thickness of the cores, copper foils and prepregs, and the effectiveness of the bonding process. We also look for any defects in the laminate after thermal stress (delamination, blistering, voids or cracks etc.)

We inspect the registration of inner copper lands to the holes. The next picture shows the same PCB as the last one, but when we measure the registration of the hole to the inner layer copper we see that there is some misalignment (in this case within tolerance).  We also use a special test coupon on all multilayer production panels to confirm the position of the drilled holes relative to the (already printed) inner layers.

There should be a robust connection between the wall of the plated through hole and the inner layer copper as shown in the next picture.  A poor or broken connection points to process issues in drilling or hole-wall cleaning.  A broken internal connection on a finished board would be caught by electrical test.

Through hole plating

We make 5 non-destructive measurements of the thickness of the plated copper in the holes on every production panel.  We back this up with regular microsectioning to get more information about process quality. For this we use the test coupon which we put on every production panel.

The plating thickness is the average of six measurements taken three on each side of the hole roughly a quarter, a half and three-quarters down.

Our standard tolerance for component holes is +/- 0,1 mm. We measure the finished hole diameters at final inspection using a tapered gauge.  Microsectioning backs this up and provides more detailed information on the quality of our processes.  The next picture shows the actual width of a plated hole with nominal diameter of 250 microns.

Copper thickness

Inner layers

Inner layers are not plated so the copper thickness is that of the copper foil used.  However, some copper is lost during the cleaning processes.  The IPC A 600 Class 2 standard gives the following values for the minimum acceptable copper foil thickness after processing:

Start copper Minimum thickness after processing
12 µm 9,3 µm
18 µm 11,4 µm
35 µm 24,9 µm
70 µm 55,7 µm

This image show the copper thickness after processing for an inner layer with 35 µm start copper:

Outer layers.

Outer layers are plated up when we plate through the holes, so that the final copper thickness is the start copper foil less any copper lost during cleaning plus the plated copper.  IPC A 600 Class 2 gives the minimum acceptable finished copper thickness after processing as:

Start copper Minimum thickness after processing
12 µm 29,3 µm
18 µm 33,4 µm
35 µm 47,9 µm
70 µm 78,7 µm

Microsectioning shows the thickness of an outer layer track with 18 µm start copper:

We can also measure separately the thickness of the base copper and of the plated copper.  The base copper foil in this case was 12 microns.

Solder mask

The minimum solder mask thickness over the copper conductors should be 8 µm.

Surface finish

We can use microsectioning to measure the thickness of Leadfree Hot Air Levelling (HAL). For electroless gold over nickel (ENIG or Che Ni/Au) we can only use microsectioning to measure the nickel thickness (as shown in the picture) as the gold thickness is under 0.1 µm. For measuring the thickness of the gold and for Immersion silver we use non-destructive X-ray measurement.

How do we assure the quality of your PCB. – part 1

Quality assurance – Part 1 : During Production

Introduction

Quality is not something that is inspected into your PCB. We build it into your boards from the moment you open the price calculator. Our smart menus guide you towards optimum manufacturability. Then PCB Visualizer checks the manufacturability of your specific data-set. We back the quality of your data by preparing the right tooling, using the right equipment, buying in the right materials, designing and implementing the right processing, and hiring and training the right operators. There’s more on this in our video: “How to make a PCB.” Operator training is critical. It is the duty of every operator to check the boards as they go through their process, and we make sure that they have the training and the expertise.

Of course, our fabrication process also include specific inspection and test steps. We use these to make sure that our processes are running correctly. These steps give you the added re-assurance that the board you receive is correct to your design and will perform correctly over the lifetime of your product. These steps are described below.

Standards

We inspect all boards to IPC-A-600 Class 2 This is the standard used for most PCBs, and is the standard most often specified by our customers. The IPC, or Institute for Printed Circuit Boards, is “a global trade association representing all facets of the industry including design, printed circuit board manufacturing and electronics assembly.” The IPC-A-600 standard “describes the preferred, acceptable and non-conforming conditions that are either externally or internally observable on printed boards”. It divides PCBs into 3 product classes. Class 2 includes “products where continued performance and extended life is required, and for which uninterrupted service is desired but not critical.” Class 3 (where uninterrupted service is critical) is used for aerospace, defence and medical applications. For more information visit www.ipc.org.

Customers, especially those supplying the US market, may also specify UL marking. In this case, we further inspect to UL796. The Underwriters’ Laboratory (UL) is “an independent global safety science company …. dedicated to promoting safe living and working environments, UL helps safeguard people, products and places in important ways, facilitating trade and providing peace of mind.” For PCBs, the most important criterion highlighted by UL marking is flammability. All our FR4 material meets UL 94 V0 plastics flammability test. For more on UL visit www.ul.com.

Inspection steps during production.

Front-end Engineering

The first step is to make sure that the data that we will use to make your PCBs is correct. To find out how we do this, go to our blog “Front-end Data Preparation

Fabrication tests

We run 3 types of test during fabrication, visual, non-destructive measurements and destructive tests. The destructive tests are used to check our processes. They are made on actual PCBs or on the test coupons which we put onto every production panel. After more than 30 years of PCB manufacturing experience, we have developed test coupons on the production panels which provide simple, non-destructive tests for more complex parameters.

Each fabrication step can be seen in our video “How to Make a PCB”. The sequence below is based on a multilayer PCB. Single- and double-sided boards do not use all these steps, but are tested in the same way.

Passport

The results of these checks are summarised for each job in its Passport which contains information on the materials used, measurements made and tests passed. You can access the Passport via the blue book icon with each job under View Running Orders once it has been inspected or under Order repeats/View history.

Traceability

If you need more information on a job, we have full traceability back to material batches etc. Contact euro@eurocircuits.com or your local sales channel for this service.

Step 1. Base material.

This is automatically checked against the order details using a data-matrix. The material data (type, manufacturer, laminate and copper foil thickness) is entered into the job history and will appear in the final Passport.

2. Print and Etch inner layers.

Visual checks.

This step includes 3 visual checks:

  1. After printing and stripping to make sure that the unwanted etch resist has been stripped away cleanly
  2. After etching to make sure that all the unwanted copper has been etched away.
  3. At the end of the process to make sure that all the etch resist has been stripped from the board.

Sample check.

Each production panel has a specially developed test coupon which indicates that the board has been correctly etched and that the track widths and isolation distances are correct. The type of etch resist used and the values for track width, isolation distances and annular ring are entered into the Passport file.

3. Inspect inner layer copper patterns.

We use Automatic Optical Inspection equipment to scan the inner layer copper and compare it to the design data. The machine checks that all track widths and isolation distances correspond to the design values and that there are no short or open circuits which will cause the finished board to malfunction.

A Pass is entered into the Passport.

4. Multilayer bonding.

Material.

This is automatically checked against the order details using a data-matrix. The material data (type, manufacturer, pre-preg and copper foil) is entered into the job history and will appear in the final Passport.

Thickness after bonding.

This is measured on each production panel and the result entered into the Passport.

5. Drilling.

The drilling machines automatically check drill diameters to ensure that the size of the holes will be correct. A special test coupon on multilayer boards confirms the position of the drilled holes relative to the (already printed) inner layers.

The smallest finished hole size is entered into the Passport.

6. Hole-wall preparation.

We deposit a layer of carbon on the walls of the holes to make them conductive for electroplating. We enter the process into the Passport.

7. Apply plating resist

Visual checks.

After printing and stripping to make sure that the unwanted plating resist has been stripped away cleanly

Type of resist is entered into the Passport.

8. Copper and tin plating.

Non-destructive sample check.

The operator measures the copper thickness in the holes at 5 or more locations on one panel from every flight bar. The result is entered into the Passport .

9. Outer layer etching

Visual checks.

After etching to make sure that all the unwanted copper has been etched away.

Sample check.

Each production panel has a specially developed test coupon which indicates that the board has been correctly etched and that the track widths and isolation distances are correct. The type of etch resist used and the values for track width, isolation distances and annular ring are entered into the Passport file.

10. Soldermask.

During process.

Visual checks:

  1. Each panel is evenly coated with soldermask ink (laquer)
  2. Alignment of soldermask phototool to the PCB

Sample checks:

The operator uses a projection microscope to check every panel to ensure that the soldermask is correctly aligned and that there are no solder-mask traces on pads.

The adhesion of the soldermask to the surface of the PCB is checked by the tape test used after legend printing.

The type of soldermask ink used is entered into the Passport data.

11. Surface finish

Sample checks on all surface finishes:

  1. The thickness is measured using an X-ray scope.
  2. We check the adhesion of the surface finish to the surface of the PCB using the tape-test after legend-printing.

100% visual inspection.

1. Lead-free hot-air levelling.

The surface must be flat and even across the PCB without any non wetting. Component holes must not be narrowed or blocked. A few via holes may be blocked if they are not covered by soldermask.

2. Electroless gold over nickel.

The finish must cover all exposed copper and have the same colour across the PCB. There must be no discolouration even in the holes

3. Chemical silver.

There must be no tarnishing or blackening.

The surface finish used is entered into the Passport, even where the order is for “Any leadfree”.

For gold and silver finishes we also enter the actual values measured.

12. Component legend.

Sample checks after curing:

The operator makes a tape test to check the adhesion of the surface finish, soldermask and legend to the surface of the PCB. We press a strip of pressure-sensitive tape across the test area and then pull it off sharply. There should be no bits of copper, surface coating, soldermask or legend ink adhering to the tape.

Visual check.

The operator checks that the legend on every board is clean and legible without blurring or smudging.

13. Electrical test.

All boards are electrically tested except single-sided boards where electrical testing is an option.

  1. Shorts and open circuits.

We build a netlist from the Gerber and drill data. We use this as a reference netlist to test all nets are tested for shorts and open circuits. A pass is recorded in the Passport. As an extra precaution, if your design system outputs IPC-D-356A netlist format include the file in your data-set. We can then use this to check the Gerber netlist against your design netlist.

  1. Inner layer registration.

A special test coupon allows us to confirm that the inner layer registration is correct.

14. Profiling and milling.

We check the size and position of the board profile and internal milling using special test coupons.

15. Final inspection.

See Part 2.

How Often Can You Raise a Eurocircuits PCB to Lead-free Soldering Temperatures?

Gold plating for edge connectors

Gold Plating over Edge Connectors

Eurocircuits offer two types of gold finish: Electroless Nickel Immersion Gold (ENIG) as a surface finish for the whole PCB, and hard plated gold over plated nickel for edge-connector fingers. Electroless gold gives excellent solderability, but the chemical deposition process means that it is too soft and too thin to withstand repeated abrasion. Electroplated gold is thicker and harder making it ideal for edge-connector contacts for PCBs which will be repeatedly plugged in and removed.


Technology

We plate the hard gold onto the PCBs after the soldermask process and before we apply the surface finish to the rest of the board. Hard-gold plating is compatible with all the other surface finishes we offer.

We first plate 3 – 6 microns of nickel onto the edge connector fingers and then on top of that 1 – 2 microns of hard gold. The plated gold is not 100% pure; it contains some cobalt to increase the wear-resistance of the surface.

We normally bevel the edge connectors to ensure easy insertion. Bevelling can be specified in the order details.

To make sure that the gold fingers align exactly with the edge-connector profile, we rout the vertical edges of the connector on the first drill run. The edges of the connector are then exactly aligned to the printed image.

In some cases one or more gold fingers are shorter than the rest, so that the longer pads connect first when the PCB inserted into the connector. This means that the shorter pads cannot be connected vertically to the plating bar. They have to make the connection needed for electroplating in another direction (see illustration. Here the blue lines represent the profile added at first drill stage and the green the final profiling).

After plating we check the adhesion of the plated nickel and gold with an industry-standard tape-test. We measure the thickness of the plated layers with a non-destructive X-ray measuring machine.

Limitations of the technology

  • The plated pads have to be on the edge of the PCB, as this is an electroplating process. There has to be an electrical connection between the plated pads and the production panel frame.
  • The maximum length of the plated pads is 40 mm as we use a standard shallow plating bath .
  • Inner layers have to be free of copper at the edge of PCB. Otherwise the bevelling could expose the copper.
  • If you want your PCBs delivered in a customer panel, the panel frame/border must be open on the edge connector side to allow us to make the connection for electroplating.
  • We can plate hard gold on two sides of PCB. But if the connectors are on the opposite sides of the PCB there has to be a minimum 150 mm between them.
  • To ensure optimum quality surface-finish, do not place any plated holes (PTH), SMD or other pads closer than 2.00 mm (80 mil) to the gold fingers – see drawing.